Automobile radio receiver



y 7, 1936. D. H. MITCHELL AUTOMOBILE RADIO RECEIVER Filed March 22, 1955 I 37: I I

412 i Q32 I I ||l||||l||||||lll| I'll-1|" IIIIIIIIIII I'II II'IIIIII 55. rectifying device.

Patented July 7, 1936 UNITE? v .,,.2 'o47 .153 i. V

,L'A QM B LE I R EIV Donald HQIMitcheII, Chicago, Ill., assignor to a Galvin" Manufacturing Corporation, Chicago, Ill.,'a corporation of-Illinois Application arch 22,

Claims.

My invention relates'to radio receivers. It relates more in, particular ;to the eliminationjof ignition interference in a radio" receiver installed in an automobile orslmilar motor driven vehicle. In the installation ofra'dio receivers inauto mobiles, it is customary to mount the chassisata convenient location on the bulk head; the speaker at a convenient location {within the passenger compartment of. the carLsOmetimes at another 0' portion of the bulk head, andthe controlzneans for the receiver at some". distance ffrom. the chassis, usually on the automobile steering post. The position is notalway s exactly asindicated, but in substantially allcasesthe chassispspeaker and power supply arese'paratelyi mounted and are interconnected bycables; "These cables are a source of interference pick-up and it is cus tomary to shield them heavily'bymeanscf continuous braided shielding material in an attempt go to avoid the interference resultingfro n the close proximity to the motor ignition system. II have found that the types of] cables heretofore" required are expensive to manufacture andjmain: tain, and further are not completely satisfactory from the noise elimination standpoint., It appears that if thereis any possibility whatsoever of stray high frequency'curre'ntsenteringany portion of the receiver injan ordinary automobile installation, such stray current ,'vvill manifest itself in, the form of noise." 1 'f The principal object ,o v my; present invention is the provision ofimproved means for eliminating noise in a radioreceiver of 'the character described. l Another object is to, avoid. objectionable stray current pick-up in the cables connecting; one portion of the installation to anothenf n Another object is to avoid the u'se'lof shielding in connecting cables. f L f Other objects and featurespf ,the invention will be apparent from ajconslderation of the following detailed description taken with' the a'c' companying drawing, i Wh 1-. a T1 The single figure is a circuit diagram showing the application of my invention toIaradio receiver but indicating, schematically certain features thereof. j In the embodiment shown,. I have applied'rny invention to; a radio installation" which employs in the receiver portion asuperheterodyne type of circuit and. a dynamic itypeof loud speaker. Power is supplied to'jthe set from the ordinary car battery; usuallysix volts, by power supply device including an interrupter;transformer and The *prsent invention con- 1933, Serial No. 652,032 (01. 2s0-20) cerns itself principally with the battery cable whichsupplies all of the power to every portion of the receiveri'and. the speaker cable which includes the conductor running to the voice' coil and the conductor running to the dynamic 5 speaker field coil. Each of these cables employs only a'single conductor for each circuit, one side of eachcircuit being grounded. The chassis itself "is mounted in a metal container. Within the chassis container and shielded from each 10 other I providea plurality of relatively very low resistance. air core choke coils through which the current passes, the coil ineach instance being part of thej 'circllit. At one side of the coil I ground the conductor through a suitably designed condenser whereby toqby-pass the high frequencies to ground.

'Consider first the battery cable and the utilization of the present invention inv connection therewith. The usual car battery It] has one terminal grounded at H and to the other terminal a conductor [2 is connected running to a main switch 53 forminga part of the receiver. .The receiveritself is placed within a shielded container [4 which is grounded at Hi to the-automobile car frame. 1 Between the main switch 13 in theend of conductor [2, I connect a choke coil I! designed to pass the battery voltage without appreciable resistance but being inductively wound to offer a resistance to high' frequency 30 currents which may be picked up on the battery cable conductor I2. On the input side'of the choke coil l'! I connect the conductor 12 to ground through a, condenser l8. With the type of circuitshown and which will lie-referred to somewhat hereinafter, I have obtained good results vvhen'the coil l1 comprised twenty turns of ,No. 14' copper wire wound on a one-half inch dowel and in which the condenser 18 had a capacity of 0.25 microfarad. Preferably a shield I9 is placed around the choke coil 11. In con- 'necting' oneside' of the condenser l8 to ground I find that'go'od' results areobtained by connecting;direct1y to-the' metal container I4. In the "preferred form, both the condenserlB and the ground connectionare arranged outside of the "container I4. I t 'ltw'ill be understood that current in the conductor I2 is normally flowing from the .battery to the power supply device. Since the power supply device includes a filter circuit, there is slight possibility of stray pick uponthe conductor l2 entering the receiver throughthe power supply device. -In'customary practice in automobile radioinstallations, however, the -sixvolt direct current from the battery is delivered directly to the heater elements of the tubes and to the field coil of the speaker. Through either connection, particularly those to the heater elements of the tubes, interference may be introduced intothe receiver unless means is employed to prevent it. Since all of the power delivered to the receiver is from the conductor,l-2, my method-of preventing stray; high frequency currmtsfromfiltering back into the receiver avoids any possibility of interference from this source. As a consequence in my installation ordinary suitablyinsul ated wire can be used in place of the usual shielded-cable.

The complete description of .the ci1 cuit employed in the receiver is not essential to an understanding of the present invention. A brief reference to portions theregf will be, made, .how= ever, to facilitate an understanding offu'rther use of the principles of the present invention. .When the switch 13 is closed, battery voltage is delivered to a conductor? I connected to onejsiide of the switch and from the conductor f 2;| "through suitable connections including jacks "22 (myocpending applic'atiom'SerialNo.6391)81Q filed October 22,1932, describes the us'eof these jacjkslto aninterrupter and converterj23, Theplate' volt; ageis supplied to .the receiver through the device 23, a portion thereof flowing'through a filter circuit as shown and a portion'beiwri unfiltered it being understood that infthefinalfstag'es the higher frequencies'will not affect the voice frequencies sufficiently .to'bejobjectionable. The circuit emp1oye is the .superheterodyne type and includes automatic volume control and other features now in common demand. The final stage is a push-pull.stageincludingtubes 24 and.26,rthe output of .Which isdeliveredthrough suitable connections shown to Van output transformer -21. The secondary gthe out-puttrans formerhaszone terminal grounded and the other terminal connected to. a conductor 1 8 running to a voice coil 29 of the speaker. [The'lpa'ker 'is indicated; schematically and includes ',a ,cone 3, .to which in customary practice-the voice;c ,oi1 i2, 9 is secured A field coil 31; employed with-the dynamic type of speaker and .hasone' endgrjound ed and the other-end connected tea conductor}; which through suitable connections supplies's'ix volt current. to the fieldcoil. In: the customary arrangement, the. conductors 28' and 32 will together constitute asingle cable, usually; termed the "speakerflcable; or-theymay be separate; cables depending; upon the particular design-of the set. ,It is customaryqprabtiocwt shieldthistypeof cable thoroughly. It-1S under.-

stood, however; that higher frequencies. picked up n the cables 28-and 32 wilt-not have anydirect effect upon the operation ,of the speaker.

#Ifhroughsuch cables or. conductors, however stra high frequencycurrents-cambeied backinto the receiver and either through inductive connections or :direct conductive connections willsoaffectjhe receiver itself as to manifest themselves in the formof noise. Iamaable to employ ally the same. arran ement on ithistypeiof conductor as described herein above in connectionw-itl'i the battery cable to preventinterference from-this source. A i. First considering the ..conducto r=- connected to the fieldtcoil, Ixemploy aneinductivelyswound grounded through a condenser to iDIQYidBi-fi high impedance path to ground through which the high frequency current will be filtered but which will not affect lower frequency current.

The feeding back of high frequency currents through the voice coil conductor 28 is prevented in the same way. A coil 31 is connected into the conductor on the inside of the chassis between the terminal of the conductor 28 and the secondary of the output transformer 21. ,This 0911.118 provided with a. shield 38 and has one side grounded through a. condenser 39. Both the cells 33 and 31 may consist of twenty turns of No. 14 copper wire wound on a one-half inch dowel. Y The-condenser 36 with the design of set whichl show preferably has a capacity of about .1 miqr0farad. .-wnile good results are obtained if the condenserjlhas a capacity of .003 microfarad. since. the source of power for an automobile 'recelver'ofthe'present design is a standard type of-isixabolt battery, I prefer to feed the battery current directly to the heater elements of the tubes. this end; aconductor 4| having a suitable'cpnnectio'nto battery through the conductor @lfis .employedito'feed the current to the heater elements of t ejtubes. as shown. I have found that a quiet" g efiect is obtained if an inductively HQWQQQQHQZ isjconnected into the conductor 4| and providedjwith asiii e u. One side of this coil g nay.be 'groundedthrough a condenser 45, if desi rjc d', but I have 'found in .some instances that theldistributed capacity of the'wires leading tof thejreceiver isysufllc'ient to balancethe inductance prenatal '42 and no separate con- .gienser, isredu ired. @The coil 42 also may consist .Q f twe" ty, turnsof No. 14 copper wire wound on a'one -half inch-dowel. 'It should be remembered that as far'as'eachofthe coils l.|,.33, 31 and 42 a.r e.concerne'd, they shquldnot be such as to inclgease' thegresistanoe, to the passage of currents normalitomthem while having suflicient resistance to.act aschokes insofar a's stray high frequency u ents'a o n erned.

.er'nplby i nglthe,'presentinvention, I can -a lo i1se.nov el means'm attenuating stray an- ,tennafpick-iip. This novel means is described in .d'etail in my eepending application, Serial No.

42,152 filedNovember 111, 1932. In order that .tl 'epn he means 'fdreli'minating noise in a receive such asf'shown may beunderstood, howeve rfi have illustrated one. means of eliminating I stray antennapickuup employing the principle descr'bed in fraye -pending application.

, n i m ain antenna .4Bfdf the .type usually carried in the roof of acar'i's employed and connected by a cenduetor lhtoone end of-thecoil 48,.the op- :46. ff the antenna 4,6 is located'in an automobile,.

"for e ample,it .fwi1ljpick.'up some or the ignition frequencies. 'Thefante'nna, 5| will then be located in a heavy 'ignitionfield, as, for example, under ti g engine hood. llhe antenna 5| has a lead-in .0011 the o positelend'c ifl the icoil' being grounded. The coils 49 and 53ar'e variably coupled so that they .can be tunedinsucha wayas to ca'use'the coil 53 to ;.buc k outor attenuate 'all .61: the undesirable frequencies impressed'upon the coil 48 by the g.ntepna 46. The coils.48.and 53 together are supported'in aeshiel d'ed,container 54. The coil 48 si iitably connected tothepriniary of a radio g-frequency-transformerwhich forms apart of the first stage of-the receiver.

to .52 connectedto oneend of the coil 53, I

I have shown the various coils employed in accordance with my present invention for suppressing interference as being separately shielded. It will be understood, however, that many different Ways of shielding these coils may be employed. In the preferred construction, I employ a metal cabinet as shown in my co-pending application, Serial No. 639,081, filed October 22, 1932, and merely provide separate compartments for each one of the coils. I1, 33, 31 and 42. These are structural features, however, and it is well understood that various structural expedients can be employed for utilizing the principles I have established.

As far as each of the by-pass condensers I8, 36, 39 and 45 are concerned, it will be well understood by those skilled in the art that I may employ any suitable means for securing the same result, namely, a high capacity impedance path to ground, so related to the choke coils as to cooperate with them. Portions of the wiring in certain cases, for example, may have sufiicient capacity effect to make the use of a separate condenser unnecessary. In other words, any electrical arrangement including an inductance and capacity can be used which together function to pass the lower frequencies but filter out or bypass the higher undesirable frequencies.

I have described my invention in detail giving actual illustrative electrical values for various portions of the apparatus, but it is obvious that I am not restricted to the specific details shown and described, and the invention is limited only by the appended claims.

What I claim as new and desire to protect by Letters Patent of the United States is:

1. In an automobile radio installation, means for suppressing the effect of undesirable outside current frequencies, a radio receiver having a grounded metal shielding cabinet, an interrupter converter power supply means within the cabinet for converting direct battery current to alternating current for plate supply, a conductor connecting a terminal of the usual automobile storage battery to said power supply means, a low resistance coil and shunt condenser connected to said battery conductor between the battery and the power supply, a dynamic speaker having a voice coil and field coil positioned outside the receiver cabinet, a connection from the speaker field coil through a radio frequency choke with a by-pass condenser to a connection from the battery but at a point beyond the first said low resistance coil and condenser whereby current is fed from the battery to the field coil through the low resistance coil and the radio frequency choke, and a radio frequency choke and by-pass condenser connected between the voice coil and the receiver.

2. In an automobile radio receiver, means for suppressing the effect of undesirable outside cur rent frequencies including a grounded metal shielding cabinet, an interrupter convertor power supply within the cabinet for converting direct battery current to provide a plate supply for the receiver, an automobile storage battery, a dynamic speaker positioned outside and independent of the shielding cabinet and having a voice coil and field coil, a single conductor from the ungrounded terminal of the storage battery extending into the receiver cabinet and connected to the interrupter convertor power supply, said battery conductor supplying all of the power to the receiver and dynamic speaker, a low resistance coil in series with said battery conductor and a shunt condenser connected to the battery conductor between the battery and said converter power supply means, a connection from the speaker field coil' to the battery supply at a point between the low resistance coil and converter power supply means, a low resistance choke coil in series with the conductor extending to the field coil with a by-pass condenser having one terminal connected to said conductor between the field coil and low resistance choke coil, and a third conductor from the voice coil of the speaker extending inside the shielding cabinet.

3. In a radio receiver system for vehicles having an ignition system, a storage battery for direct current supply to said receiver system and said ignition system, a radio receiver in said receiver system, and an externally mounted loud speaker, external current supply lines to said radio receiver and to said loud speaker, and means in said lines for eliminating ignition interference picked up by said lines to prevent said interference from entering said radio receiver, said means comprising a radio frequency filter in each of said lines including an inductance and a capacitance.

4. In aradio receiver system for vehicles having an ignition system, a storage battery for direct current supply to said receiver system and said ignition system, a radio receiver in said receiver system, and an externally mounted loud speaker having a voice coil and a field coil, external current supply lines to said radio receiver, said voice coil and said field coil and means in each of said lines for eliminating interference picked up by said lines to prevent said interference from entering said radio receiver, said means comprising a filter in each of said lines including an inductance and a capacitance.

5. In a radio receiver system for vehicles having an ignition system, a storage battery common to said receiver system and ignition system, a radio receiver chassis having a receiver circuit thereon, a loud speaker employing a field coil and voice coil mounted on said vehicle away from said radio receiver, and an antenna for said receiver system external of said radio receiver chassis, external supply lines from said antenna to said receiver circuit, from said battery to said receiver circuit, and to said speaker voice coil and to said speaker field coil, means for eliminating ignition interference picked up on said external circuits and preventing the same from entering the receiver circuit, said means including a balancing unit comprising a pair of variably coupled inductance coils in electrical connection in the line from the antenna to said receiver, and a radio frequency filter in electrical connection in each, the supply line between the battery and the radio receiver circuit, the supply line between the speaker field coil and receiver circuit, the supply line between the speaker voice coil and receiver circuit.

DONALD H. MITCHELL. 

